[New-bugs-announce] [issue40749] Consider adding decorator for required inner class

[Elijah Rippeth]

New submission from Elijah Rippeth <elijah.rippeth at gmail.com>:

Sometimes it's desirable to couple classes together by nesting. Currently there's no way to signal to an interface implementer that an inner class is a required attribute to be implemented. 

I propose a decorator for `abstractnestedclass` to fill this gap. A simple example use-case is outlined below:

```
from abc import ABCMeta, abstractnestedclass

class BaseComponent(metaclass=ABCMeta):
    @abstractnestedclass
    class Config:
        pass

class MissingNestedComponent(BaseComponent):
    # This will raise when constructed because 
    # BaseComponent.Config is not implemented
    pass

class NonraisingComponent(BaseComponent):
    # This will be constructable
    class NonraisingComponentConfig(BaseComponent.Config):
        pass
    pass
```

----------
components: Library (Lib)
messages: 369756
nosy: Elijah Rippeth
priority: normal
severity: normal
status: open
title: Consider adding decorator for required inner class
type: enhancement

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40749>
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